The present invention relates to an axial-flow rotary blood pump that can be implanted into the chest of a human and can be used to assist a human heart in pumping blood.
One application of blood pumps is to boost blood circulation in patients whose heart still functions but is not pumping blood at an adequate rate. The estimated need for a relatively simple, long-term ventricle assist device (VAD) is presently projected at between 50,000 and 100,000 patients per year in the United States alone.
Despite this need, prior pumps have not been entirely satisfactory due to a variety of problems. For example, fluid dynamic forces in the pump may activate platelets, leading to formation of blood clots. High shear stresses in the pump may damage red blood cells. These problems can be exacerbated by the small size required for a blood pump to be implantable, which necessitates a high rotational speed in a rotary type pump. Further, some prior devices have required large external support equipment, resulting in little or no patient mobility.
Problems of prior pumps that have limited their clinical use to relatively short times include the following: (1) blood damage which may occur when blood comes into contact with rotor bearings, (2) the need for bearing purge systems which may require percutaneous (through the skin) saline solution pump systems, (3) bearing seizure resulting from the considerable thrust and torque loads, or from dried blood sticking on the bearing surfaces, (4) problems of blood damage (hemolysis) and blood clotting (thrombosis) caused by relative rotational movement of the components of the pump, (5) pump and control size and shape limitations necessary for implantation or convenient mobility, (6) weight limitations for implantation to avoid tearing of implant grafts due to inertia of sudden movement, (7) difficulty in coordinating and optimizing the many pump design parameters which may affect hemolysis, (8) high power consumption that requires a larger power supply, (9) motor inefficiency caused by a large air gap between motor windings and drive magnets, (10) heat flow from the device to the body, (11) complex Hall Effect sensors/electronics for rotary control, (12) the substantial desire for minimizing percutaneous (through the skin) insertions, including support lines and tubes, (13) large pump and related hose internal volume which may cause an initial shock when filled with saline solution while starting the pump, and (14) high cost effectively makes the device unavailable for many patients who could otherwise benefit from it.
Although significant efforts have been made to solving the problems associated with implantable blood pumps, there is still a great need for an improved pump that can be used for an extended period in a human as a ventricle assist device, and that is reliable, compact, relatively inexpensive, requires limited percutaneous insertions, and produces fewer blood clots and less blood damage problems.